1. Field of the Invention
The present invention relates to a foil-decorating injection molding method that molds decorative sheet carrying patterns and characters into a molding in a mold by injection molding to produce a molding decorated with the patterns and the characters, and a foil-decorating injection molding apparatus for carrying out the foil-decorating injection molding method.
2. Description of the Related Art
There have been proposed many foil-decorating injection molding methods that mold a decorative sheet carrying patterns and characters into a molding in a mold by injection molding to produce a molding decorated with the patterns and the characters. Most of those previously proposed foil-decorating injection molding methods carry out all or some of the following processes (a) to (i) in that order or in order of a sequence different from that of the processes (a) to (i) sequentially or some of those processes are carried out simultaneously or parallelly.
Process (a): A decorative sheet feed process for feeding a decorative sheet onto a parting surface of a female mold of an injection mold employed in injection molding PA1 Process (b): A sheet clamping process for clamping the decorative sheet to hold the decorative sheet fixedly on the parting surface of the female mold PA1 Process (c): A softening process for heating and softening the decorative sheet by a hot plate or the like PA1 Process (d): A drawing process for drawing the softened decorative sheet by vacuum forming and/or pressure forming so that the decorative sheet may conform to the inner surface of the female mold (Preparatory molding process) PA1 Process (e): A mold closing process for closing the injection mold by moving the female mold to a male mold or by moving the male mold to the female mold PA1 Process (f): An injection molding process for injecting a fluid resin (molten resin) through the male mold into a cavity defined by the male mold and the female mold PA1 Process (g): A mold opening process for separating the male mold and the female mold PA1 Process (h): A trimming process for removing marginal portions of the decorative sheet PA1 Process (i): An ejecting process for ejecting the molding decorated with the decorative sheet from the female mold
In a simultaneous process implementation mode, the plurality of processes are carried out simultaneously. For example, the process (b) for clamping the decorative sheet and the process (e) for closing the mold are accomplished simultaneously if the decorative sheet is held between the male mold and the female mold in the mold closing process. The process (d) for drawing the decorative sheet and the process (f) for injecting the molten resin into the injection mold can simultaneously be accomplished if the decorative sheet is drawn by the heat and the pressure of the molten resin injected into the injection mold.
A laminated decorative sheet or a transfer decorative sheet is used selectively depending on the type of product to be produced. If a laminated decorative sheet is used, the laminated decorative sheet is attached integrally to the surface of an injection-molded molding to form a decorative layer. If a transfer decorative sheet having a substrate and a decorative transfer layer formed on the substrate is used, the transfer decorative sheet is attached to the surface of a molding, and then the substrate is removed from the molding, so that only the decorative transfer layer remains on the surface of the molding.
In the conventional foil-decorating injection molding method comprising the foregoing processes, the tension of the decorative sheet is kept constant during the sheet feed process, at the start of the sheet clamping process and at a moment immediately before the completion of the sheet clamping process, or the tension of the decorative sheet is increased in the sheet clamping process subsequent to the feed of the decorative sheet onto the parting surface of the female mold, which is described in, for example, JP-B No. 1-59095 and JP-U No. 4-34004. The decorative sheet is broken sometimes when the same is clamped if the decorative sheet is tautened excessively or the decorative sheet sometimes is slackened to crease or the decorative sheet is dislocated from a correct position if the decorative sheet is excessively slack.
As mentioned in JP-A No. 7-227877, when a molding to be produced is, for example, a control panel P as shown in FIG. 8(A) for a rice boiler, having the shape of a curved surface having a relatively great height and resembling a portion of a circular cylinder, an injection molding apparatus sometimes employs a special clamper 25 as shown in FIG. 8(B). The special clamper 25 has a frame-shaped clamping part 25a having the shape of a frame to press and hold a decorative sheet on the parting surface of the female mold, and a sheet pressing part 25b having the shape of a two-dimensional curved surface to press part of the decorative sheet into a recess formed in the female mold. When the special clamper 25 is employed, it is possible that a further problem arises in addition to the foregoing problems; that is, the tension of a decorative sheet S increases sharply as the special clamper 25 presses the decorative sheet S to clamp and hold the decorative sheet S and, as shown in FIG. 8(C), portions of the opposite sides of the decorative sheet S slip off the opposite side members of the frame-shaped clamping part 25a into the recess as shown in FIG. 8(C) and, consequently, the decorative sheet cannot properly be clamped.